Network Working Group M. Gupta
Internet Draft Nokia
Document: draft-ietf-ospf-ospfv3-auth-01.txt N. Melam
Expires: October 2003 Nokia
April 2003
Authentication/Confidentiality for OSPFv3
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 10 of RFC2026.
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Abstract
This document describes means/mechanisms to provide
authentication/confidentiality to OSPFv3 using IPv6 AH/ESP Extension
Header.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [5].
Table of Contents
1. Introduction...................................................22. OSPFv2 to OSPFv3...............................................23. Authentication.................................................24. Confidentiality................................................35. Authentication and Encryption Algorithms.......................36. Key Management.................................................3M. Gupta/N. Melam Expires - October 2003 [Page 1]

Authentication/Confidentiality to OSPFv3 April 20037. SA Granularity and Selectors...................................48. Virtual Links..................................................59. IPsec rules....................................................510. Replay Protection.............................................6
Security Considerations...........................................6
References........................................................7
Acknowledgments...................................................7
Authors' Addresses................................................71. Introduction
In OSPFv3 for IPv6, authentication fields have been removed from OSPF
headers. When running over IPv6, OSPF relies on the IPv6
Authentication Header (AH) and IPv6 Encapsulating Security Payload
(ESP) to ensure integrity, authentication and/or confidentiality of
routing exchanges.
This document describes how IPv6 AH/ESP extension headers can be used
to provide authentication/confidentiality to OSPFv3.
It is assumed that the reader is familiar with OSPFv3 [1], AH [4],
ESP [3], the concept of security associations, tunnel and transport
mode of IPsec and the key management options available for AH and ESP
(manual keying and IKE) [2].
2. OSPFv2 to OSPFv3
Security concerns MUST be taken away from OSPFv3 protocol and IPv6
stack MUST provide inherent security to OSPFv3 by using AH/ESP
extension headers. It means OSPFv3 protocol MUST not receive any
unauthenticated packets. As OSPFv2 has its own security mechanisms,
no inherent security needs to be provided by the IPv4 stack. As
OSPFv2 is only for IPv4 and OSPFv3 is only for IPv6, the distinction
between the packets can be easily made by IP version.
Authentication and confidentiality, if provided, MUST be provided to
the entire OSPFv3 header and data. Authentication to the selected
portions of IPv6 header, selected portions of extension headers and
selected options may also be provided optionally.
3. Authentication
Transport mode SA is the security association between two hosts or
security gateways that are acting as hosts. SA must be tunnel mode if
either end of the security association is a security gateway. OSPFv3
packets are exchanged between the routers but as the packets are
destined to the routers, the routers act like host in this case. So
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Authentication/Confidentiality to OSPFv3 April 2003
transport mode SA MUST be used in order to provide required security
to OSPFv3.
In order to support OSPFv3 authentication, "ESP with NULL encryption"
MUST be supported in transport mode. "AH" in transport mode SHOULD
also be provided. AH in transport mode provides authentication to
higher layer protocols, selected portions of IPv6 header, selected
portions of extension headers and selected options. ESP with NULL
encryption in transport mode will provide authentication to only
higher layer protocol data and not to the IPv6 header, extension
headers and options.
OSPF packets received in clear text and OSPF received with incorrect
AH ICV MUST be dropped when authentication is enabled.
4. Confidentiality
Providing confidentiality to OSPFv3 in addition to authentication is
optional. Confidentiality must be implemented using ESP extension
header of IPv6 if it is being provided. ESP with non-null encryption
in transport mode MUST be used for the providing confidentiality to
OSPFv3.
5. Authentication and Encryption Algorithms
The implementations MUST be conformant to the RFCs that describe
mandatory-to-implement algorithms for use with ESP and AH.
6. Key Management
OSPFv3 exchanges both multicast and unicast packets. While running
OSPFv3 over a broadcast interface, the authentication/confidentiality
required is "one to many". Since IKE is based on the Diffie-Hellman
key agreement protocol and works only for two communicating parties,
it is not possible to use IKE for providing the required "one to
many" authentication/confidentiality. Manual keying MUST be used for
this purpose. In manual keying SAs are statically installed on the
routers and these static SAs are used to encrypt/authenticate the
data.
Since security associations (SAs) are directional, generally
different security associations are used for inbound and outbound
processing for providing higher security. The following figure
explains that it is not possible to use different security
associations for inbound and outbound processing in order to provide
the required "one to many" security.
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Authentication/Confidentiality to OSPFv3 April 2003
A |
SAa ------------>|
SAb <------------|
|
B |
SAb ------------>|
SAa <------------|
|
C |
SAa/SAb ------------>|
SAa/SAb <------------|
Broadcast
Network
If we consider communication between A and B in the above diagram,
everything seems to be fine. A uses security association SAa for
outgoing packets and B uses the same for incoming packets and vice
versa. Now if we include C in the group and C sends a packet out
using SAa then only A will be able to understand it or if C sends the
packets out using SAb then only B will be able to understand it.
Since the packets are multicast packets and they are going to be
processed by both A and B, there is no SA for C to use so that A and
B both can understand it.
The problem can be solved with the following figure where all of them
use the same SA for incoming and outgoing direction.
A |
SAs ------------>|
SAs <------------|
|3
B |
SAs ------------>|
SAs <------------|
|
C |
SAs ------------>|
SAs <------------|
Broadcast
Network
So, all the adjacent routers on a broadcast medium MUST use the same
SA and the same SA MUST be used for inbound and outbound processing.
7. SA Granularity and Selectors
The user SHOULD be given a choice to share the same SA among multiple
interfaces or using unique SA per interface.
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Authentication/Confidentiality to OSPFv3 April 20038. Virtual Links
Different SA than the SA of underlying interface MUST be provided for
virtual links. Packets sent out on virtual links use unicast site
local or global IPv6 addresses as the IPv6 source address and all the
other packets use multicast and unicast link local addresses. This
difference in the IPv6 source address should be used in order to
differentiate the packets sent on interfaces and virtual links.
As the end point IP addresses of the virtual links are not known at
the time of configuration, the secure channel for these packets need
to be setup dynamically. The end point IP addresses of virtual links
are learnt during the routing table build up process. The packet
exchange over the virtual links starts only after the discovery of
end point IP addresses. In order to provide security to these
exchanges, the routing module should setup a secure IPsec channel
dynamically once it acquires the required information.
According to the OSPFv3 RFC, the virtual neighbor's IP address is set
to the first prefix with the "LA-bit" set from the list of prefixes
in intra-area-prefix-LSAs originated by the virtual neighbor. But
when it comes to choosing the source address for the packets that are
sent over the virtual link, the RFC simply suggests using one of the
router's own site-local or global IPv6 addresses. In order to install
the required rules for virtual links, the source address also needs
to be predictable. So the router MUST use the first prefix with the
"LA-bit" set from the list of its own intra-area-prefix-LSAs as the
source address of the packet. This makes both the source and
destination address of the packets exchanged over the virtual link,
predictable on both the routers.
9. IPsec rules
The following set of rules can be installed in a typical IPsec
implementation to provide the authentication/confidentiality to
OSPFv3 packets.
Outbound Rules for interface running OSPFv3 security:
No. interface source destination protocol action
1 iface fe80::/10 any OSPF apply
2 any src/128 dst/128 OSPF apply
Inbound Rules for interface running OSPFv3 security:
No. interface source destination protocol action
3 iface fe80::/10 any ESP or AH apply
4 iface fe80::/10 any OSPF drop
5 any src/128 dst/128 ESP or AH apply
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Authentication/Confidentiality to OSPFv3 April 2003
6 any src/128 dst/128 OSPF drop
For outbound rules, action "apply" means encrypting/calculating ICV
and adding ESP or AH header. For inbound rules, action "apply" means
decrypting/authenticating the packets and stripping ESP or AH header.
Rules 4 and 6 are to drop the in-secure OSPFv3 packets without ESP/AH
headers.
Rules 2, 5 and 6 are meant to secure the packets being exchanged over
virtual links. These rules are dynamically installed after learning
the end point IP addresses of a virtual link. These rules MUST be
installed on at least the interfaces that are connected to the
transit area for the virtual link. These rules MAY alternatively be
installed on all the interfaces. If these rules are not installed on
all the interfaces, clear text or malicious OSPFv3 packets with same
source and destination addresses as virtual link end point addresses
will be delivered to OSPFv3. Though OSPFv3 drops these packets
because they were not received on the right interface, OSPFv3
receives some clear text or malicious packets even when the security
is on. Installing these rules on all the interfaces insures that
OSPFv3 does not receive these clear text or malicious packets when
security is turned on. On the other hand installing these rules on
all the interfaces increases the processing overhead on the
interfaces where there is no IPsec processing otherwise. The decision
of installing these rules on all the interfaces or on just the
interfaces that are connected to the transit area is a private
decision and doesn't affect the interoperability in any way. So this
decision is left to the implementers.
Rules 1, 3 and 4 are meant to secure the unicast and multicast
packets that are not being exchanged over the virtual links. These
rules are interface specific.
10. Replay Protection
As it is not possible as per the current standards to provide
complete replay protection while using manual keying, the proposed
solution will not provide protection against replay attacks.
Fields LS age, LS Sequence Number and LS checksum in LSA header are
kept intact in OSPFv3. Though these fields do not provide the
complete protection, they certainly help against replay attacks.
Security Considerations
This memo discusses the use of IPsec AH and ESP headers in order to
provide security to OSPFv3 for IPv6.
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